Using crack arrestor for inhibiting damage from dicing and chip packaging interaction failures in back end of line structures

ABSTRACT

A semiconductor product comprises a semiconductor substrate having a top surface and a bottom surface including a semiconductor chip. The semiconductor substrate has a top surface and a perimeter. A barrier is formed in the chip within the perimeter. An Ultra Deep Isolation Trench (UDIT) is cut in the top surface of the chip extending down therein between the perimeter and the barrier. A ILD structure with low-k pSICOH dielectric and hard mask layers is formed over the substrate prior to forming the barrier and the UDIT. The ILD structure interconnection structures can be recessed down to the substrate aside from the UDIT.

BACKGROUND OF THE INVENTION

The present invention relates to Integrated Circuit (IC) semiconductordevices and structures and methods for the manufacture thereof. Moreparticularly it relates to a process of forming structural features onsemiconductor wafers resistant to cracking within the interconnectstacks. The structural features are adapted to prevent damage tosemiconductor devices caused by subdivision of semiconductor wafers intoindividual chips by a process known as dicing. In addition, thisinvention relates to prevention of chip packaging interaction fails ininterconnect structures formed during Back End Of Line (BEOL),interconnect, processing of semiconductor devices, late in themanufacturing process.

Microelectronic semiconductor IC devices such as Complementary MetalOxide Semiconductor Field Effect Transistor (CMOS FET) devices and thelike are manufactured in a complex process in which numerous separateelectronic devices are formed. Such processes of manufacture, whichproduce large numbers of such electronic devices, are referred to asVery Large Scale Integration (VLSI) processes. After many processingsteps, the monolithic, semiconductor wafers must be subdivided by dicingto form the numerous, individual semiconductor chips.

Referring to FIG. 1A a schematic, sectional, fragmentary, elevation isshown of a prior art type of CMOS FET, monolithic, semiconductor device10 in an advanced stage of manufacture of the type which includesnumerous VLSI electronic IC devices. However, for convenience ofillustration and explanation, the only portion of the semiconductordevice 10 that is shown in FIG. 1A includes a first chip 10A which isjuxtaposed with a second chip 10B. Those two chips represent a largenumber of such chips included elsewhere in the semiconductor device 10.Semiconductor devices including the first chip 10A and the second chip10B are formed in the active device Front End Of Line (FEOL) regionwithin a semiconductor substrate 12 and upon the top surface 16 thereof.The substrate 12 usually comprises a single silicon (Si) semiconductorwafer. FIG. 1B shows the first chip 10A separated from the second chip10B, after performing a dicing step, as described below.

Initially, an active device FEOL region 14 (shown in an abstract form asa layer with features obscured) is formed on the top surface 16 of thesubstrate 12 during FEOL processing, prior to BEOL processing. Theactive device FEOL region 14 contains structures, e.g. CMOS FET devices(not shown for convenience of illustration) some of which are formed inthe substrate 12 and some of which are formed upon the top surface 16thereof. As will be well understood by those skilled in the art, it isconventional for a CMOS FET device to reach above the top surface 16 ofthe substrate 12. Subsequently, during Back End Of Line (BEOL)processing steps, an interconnect layer 15 (also shown in an abstractform as a layer for convenience of illustration) is formed over the topsurface 17 of the active device layer 14. The interconnect layer 15contains metallic structures, typically composed of copper, that provideexternal interconnections (interconnects) which are formed in manylevels of Intra-Level Dielectric (ILD) layers (i.e. an ILD stack) forelectrically connecting the numerous FET devices, e.g. the firstsemiconductor chip 10A (on the left) and the second semiconductor chip10B (on the right) to external devices, as will be illustrated in FIGS.5A/5B, etc. and described below with reference thereto. The interconnectlayer 15 includes a left side portion 15A and a right hand portion 15Bwhich are to be separated by dicing. The result of such dicing is shownin FIG. 1B.

At the base of the first chip 10A (on the left of FIGS. 1A/1B) is afirst substrate portion 12A supporting a first active device layer 14Aon surface 16 thereabove. Similarly, the left side portion 15A of theinterconnect layer 15 is formed above the first active device layer 14A.At the base of the second chip 10B, on the right, is a second substrateportion 12B supporting a second active device layer 14B on surface 16thereabove. Similarly, the right side portion 15B of the interconnectlayer 15 is formed above the second active device layer 14B. A dicingchannel 130 shown in phantom in FIG. 1A prior to dicing is located inthe space between the first and second chips 10A/10B. FIG. 1B shows thedicing channel 130 after the step of dicing has been performedseparating the chip 10A from the chip 10B. Although it is not shown, forconvenience of illustration, the dicing channel 130 surrounds each ofthe chips as is well known to those skilled in the art.

In addition, separate first and second crackstops 50A/50B are formed inthe interconnect layers 15A/15B surrounding the perimeter of eachinterconnect layer 15A/15B. Each of the first and second crackstops50A/50B is located between the dicing channel 130 and the active area(AA) of each of the chips 10A/10B, respectively. The crackstops 50A/50Bare provided along the perimeters of the chip 10A and chip 10B toprotect each interconnect layer 15A/15B from damage that would otherwisebe likely to be caused by cracking. Each of the crackstops 50A/50Bextends entirely through the interconnect layer 15 to the top surface 17of the active device layer 14.

As is conventional in BEOL processing, at least one layer of dielectricmaterial is formed in the interconnect layer 15 over the active deviceFEOL region 14 of the semiconductor device 10. Generally, such adielectric layer(s) is fabricated so that metal interconnect lines(described below) may be formed thereon to provide external electricalconnections to the FET devices. Copper, tungsten, and aluminum, oralloys thereof, and other like metals are commonly used to form theinterconnect lines. IC chips having multiple bonded dielectric layers aswell as multiple layers of interconnect lines disposed thereon are wellknown in the art.

Often the density of the material of the dielectric layers is notuniform throughout. Film stresses and interfaces in the material allowmicrocracks to propagate within the dielectric layers until themicrocracks encounter metal structures, e.g. vertically extending viasand horizontally extending interconnect lines. Because such metalstructure are very thin, such cracks usually severely affectinterconnect lines and vias causing fracture thereof resulting in chipfailure since the external connections to chip elements have beenbroken. The dicing process often causes cracks that damage active areasof chips such as chips 10A/10B. Thus to prevent such catastrophicdamage, as is conventional, crackstops 50A/50B are provided along theperimeter of the BEOL structures 15A/15B of each of the chips 10A/10B toprotect them from potential damage caused by cracking.

The manufacture of devices such as the semiconductor device 10 requiresthe performance of many preliminary steps, such as FEOL steps that formthe active device FEOL region 14 in the substrate 12 and thereabovefollowed by BEOL step during which the interconnect layer 15 is formedover the active device layer 14.

Eventually after performance of many FEOL and BEOL processing steps themonolithic, semiconductor device 10 containing the numerous, VLSIsemiconductor chips is subdivided by a dicing process to formindividual, separate chips. During the dicing process the chips whichhave been formed on the substrate 12 are separated from each other. Forexample the first chip 10A is separated from the second chip 10B. Thedicing process is confined to making cuts in intermediate spaces such asthe dicing channels 130, which are located between the first chip 10Aand the second chip 10B.

In FIG. 1B, as stated above, the first chip 10A is shown separated fromthe second chip 10B, after performing a conventional dicing stepperformed by cutting down through the semiconductor device 10 from thetop surface 18 of the BEOL structure 15 to the bottom surface 19 of thesubstrate 12 within the dicing channel 130 between the chips 10A/10Bwith the cut at the location of the dicing channel extending all the waydown through the bottom surface of the substrate 12. During dicing, aset of peripheral diced chip edge surfaces 110 are formed on thevertical edges of each of the chips 10A/10B approximately along the edgeof the chip-to-chip dicing channel 130 on the sidewalls of the dicedchips 10A/10B where material has been removed.

Manifestly, the dicing process is destructive because it generatesstresses and strains which often induce microcracks in the semiconductorsubstrate 12, the active device layer 14, and/or the dielectric layersin the interconnect layer 15. As microcracks occur in a siliconsubstrate 12 they usually propagate very rapidly thereby causingfailures that show up in the initial testing. Microcracks in layers ofdielectric material such as those found in the interconnect layers 15propagate more slowly and tend to lead to delayed failures includingchip packaging interaction fails, i.e. failures which occur afterdevices are in the field. Chip packaging interaction failures, as wellas failures in the field, are very expensive and disruptive. Thus thereis a very significant need to provide a process that reduces propagationof microcracks in dielectric layers.

A high priority goal of VLSI manufacturing is production of a high yieldof chips from each wafer, thereby assuring commercial profitability. Asthe number and complexity of chips per wafer increases, the yield oftendecreases proportionally. Accordingly, it is highly desirable tominimize the number of defective chips.

In the FEOL steps, electronic devices such as CMOS FET devices areformed by a series of steps including creation of photolithographicmasks which used to form patterns on the semiconductor substrate 12.Etching and deposition is performed with materials being introduced inblanket form onto exposed surfaces in, on, and/or above the substrate 12by deposition or growth of materials in blanket form or in specificregions by introduction of material onto surfaces through open maskwindows. In other steps, material is removed from surfaces andstructures subtractively, e.g. by etching with or without etchingthrough open mask windows.

In the BEOL processing steps, the IC fabrication process continues bybuilding interconnects containing multiple layers of wiring anddielectric passivation layers on the top surface 17 of the active deviceFEOL region 14 that contains the semiconductor devices. As stated above,the metallic structures for providing external interconnections(interconnects) are formed in many levels of ILD layers for electricallyconnecting the numerous devices on the semiconductor chips 10A/10B toexternal devices using similar processing techniques. The conventionalbarrier structures 50A/50B in FIGS. 1A/1B, known as crackstop/MOB(Moisture Oxidation Barrier) structures, are formed on the periphery ofthe interconnect layers 15A/15B of each chip 10A/10B adjacent to thedicing channel 130 where the dicing is to occur. In fact a conventionalbarrier structure 50A/50B may comprise a crackstop or MOB structure.Then upon completion of substrate-level FEOL and BEOL processing, thesemiconductor devices 10A/10B are ready to be divided into individualsemiconductor chips by dicing through the dicing channel 130 to provideseparation into individual chips including the first chip 10A and thesecond chip 10B.

As stated above, FIG. 1B depicts the prior art semiconductor device 10of FIG. 1A after dicing thereof, during which the semiconductor device10 has been split into the first chip 10A and the second chip 10B bycutting through the layers of the device in dicing channel 130 betweenthe first and second chips 10A/10B. The result of the dicing process isthat the active device FEOL region 14 and the interconnect stack 15 ofFIG. 1A are split in two. On the left the first chip 10A includes afirst active device 14A and a first chip interconnect 15A. On the rightthe second chip 10B includes a second active device 14B and a secondchip interconnect 15B. However, as stated above, the problem with dicingof semiconductor devices is that the dicing process generates stressesand strains which can lead to cracking. The dicing process often causescracks that damage Active Areas (AA) of the chips. Such cracking candamage the devices and metallization on the semiconductor chips. Toprevent such damage, the crackstops 50A/50B have been provided along theperimeter of the chips 10A/10B to interrupt propagation of cracks beyondthem.

As stated above, dicing damage causes cracking within the interconnectstacks 15A/15B of ILD and metallization layers. Such dicing-initiatedcracking can affect one or more of the many ILD layers in a BEOLstructure 15, resulting in a loss of structural integrity. The crackingproblem is exacerbated upon a subsequent step of joining semiconductorchips 12A/12B, etc. to packaging substrates. Moreover, the problem is atits worst when the packaging substrate comprises an organic material ascompared with a ceramic packaging substrate. The delta value of theCoefficient of Thermal Expansion (CTE) mismatch between differentassembled materials in the device being manufactured causes greaterstrains and stresses on the semiconductor chips, which, in turn,generate the growth of cracks within layers in a BEOL structure.

An object of this invention is to provide a structure that inhibitscracks from damaging the BEOL structure of a chip or even inhibitscracks from damaging the Active Area below the BEOL structure in thechip.

The active areas AA of the chips 10A/10B are located in each of the twosubstrate regions 12A/12B, including both the interconnect stack 15A/15Band the active device layer 14A/14B and inside the crackstops 50A/50B. Atypical crackstop 50A/50B is a solid metal structure formed in a trenchspanning all interconnect levels or a plurality of solid metalstructures spanning all interconnect levels around the periphery of eachchip on a semiconductor wafer.

New Failure Mechanisms

In the past, the weakest material in an IC structure has been thematerial of the substrate 12, which is typically composed of asemiconductor material such as monocrystalline silicon. However, theincreased demand for improvement in the performance of ICs has led tothe introduction of low dielectric constant (low-k) ILD layers in theinterconnect stack 15. The low-k materials have less mechanical(cohesive) strength than traditional dielectrics such as silicon dioxide(SiO₂).

In particular, FIG. 2A is a chart which shows that the cohesive strengthvalue of an ILD layer of a semiconductor chip decreases as a function ofdecreasing of the dielectric constant value. There is a problem, thatthe contemporary strategy of lowering of the cohesive strength of theILD layer has resulted in the shifting of the location of the weakestmaterial in an integrated structure from the substrate (which istypically monocrystalline silicon) to the ILD layers. Thus, the resultof the strategy of use of low-k materials in the ILD layer hasintroduced new failure mechanisms during the steps of dicing of wafersinto chips and subsequent packaging and reliability testing.

A key requirement for stopping these new failure mechanisms is to limitthe propagation distance, i.e. the Delamination Length (DL), to which aflaw generated during the dicing process can propagate before itencounters the crackstop/MOB structure. While there are a number ofpotential solutions to this problem, in the past solutions which havebeen employed have required either a loss in productivity (reduction innumber of chips per wafer) or a loss in I/O density due to a redesign ofa Controlled Collapse Chip Connection (C4) layouts.

FIG. 2B is a chart which shows the energy imparted to dielectric layersdue to the packaging material as a function of the defect size, i.e.length, of a flaw which is created during dicing and which propagatesduring reliability stressing. As the flaw extends to greater lengths,there is a monotonic increase in the energy release rate tending todrive the flaw towards failure. If a flaw is allowed to grow largeenough, sufficient energy will build up to (first) either break throughthe crackstop/MOB structure or (second) dive down into the silicon (Si)substrate and into the Active Area (AA) of the chip. Therefore the mostrobust path to ensuring reliability is to limit the flaw size.

Commonly assigned U.S. Pat. Nos. 5,530,280 and 5,665,655 of White, bothentitled “Process for Producing Crackstops on Semiconductor Devices andDevices Containing the Crackstops” describe a process for makingsemiconductor device with a crackstop formed by a groove filled withmetal surrounding the active region on a chip at the same time as otherfunctional metallization is occurring. Then after final passivationselective etching removes the metal in the groove. The groove passesthrough the surface dielectric or the semiconductor substrate, or isreplaced by hollow metal rings stacked through multiple dielectriclayers.

Underfill layers have been employed in IC packaging to protect theSurface Mount Devices (SMDs), i.e. IC chips bonded to a Printed Circuit(PC) board with solder ball joints. During the mounting process, thesolder balls on SMD IC chips are aligned with electrical contact pads onthe PC board. Subsequently the PC board is heated causing the metal ofthe solder ball joints to flow, joining the chips with contact pads onthe PC board. Next an underfill epoxy material is introduced between thechip and the board. Then the PC board is reheated to cure the epoxy,forming a seal around the chip to protect it from moisture and to helpto preserve the integrity of the solder balls joints.

U.S. Pat. No. 6,822,315 of Kelkar et al. entitled “Apparatus and Methodfor Scribing Semiconductor Wafers Using Vision Recognition” refers toU.S. Pat. No. 6,245,595 entitled “Techniques for Wafer Level Molding ofUnderfill Encapsulant,” as describing use of a cured or a partiallycured epoxy underfill type of layer on the top surface of a wafer beforeit is diced rather than after dicing and before mounting on a PC board.The epoxy layer, that protects the chips during handling, is formed onthe top surface of the wafer and includes an epoxy resin, a hardener, acatalyst, a filler material (e.g. silicon particles) and a dye. Thefiller material reduces the CTE of the epoxy to match that of the PCboard upon which the micro SMDs will be mounted. As temperaturevariations occur, the PC board and epoxy expand and contract at similarrates. Without the filler material, the rates of expansion andcontraction would be different, resulting in potential joint failures,over time.

Commonly assigned U.S. Pat. No. 6,566,612 B2 of Brouillette et alentitled “Method for Direct Chip Attach by Solder Bumps and an UnderfillLayer” states that in a conventional flip chip process, an underfillmaterial with thermal expansion characteristics which are CTE matched tosolder by using fillers in the underfill composition is frequentlydispensed after chip-substrate attach by a capillary action through thegap between the chip and the substrate.

U.S. Patent Application 20060125119 of Xiao et al. entitled “B-StageableUnderfill Encapsulant and Method for its Application” describes severalcompositions of underfill materials applied directly onto semiconductorwafers before dicing the wafers into individual chips.

U.S. Pat. No. 6,492,247 B1 of Guthrie et al. (commonly assigned)entitled “Method for Eliminating Crack Damage Induced By DelaminatingGate Conductor Interfaces In Integrated Circuits” describes managingcrack damage in the ICs to reduce or eliminate crack propagation intothe IC active array by providing a defined divide or separation of theIC gate conductor from the IC crackstop or edge. The method is employedto manage crack damage induced through the delamination of one or moreof the gate conductor surface interfaces as a result of the IC waferdicing process.

Commonly assigned U.S. Patent Application No. 2004/0129938 A1 of Landerset al. entitled “Multi-Functional Structure for Enhanced ChipManufacturibility & Reliability for Low K Dielectrics Semiconductors anda Crackstop Integrity Screen and Monitor” describes an on-chip redundantcrackstop providing a barrier to prevent defects, cracks, delaminations,and moisture/oxidation contaminants from reaching active circuitregions. Conductive materials in the barrier structure permit wiring thebarriers out to contact pads and device pins for coupling a monitordevice to the chip to monitor barrier integrity.

U.S. Patent Application No. 2005/0208781 A1 of Fitzsimmons et al.(commonly assigned) entitled “Crackstop With Release Layer For CrackControl In Semi-conductors” describes forming an IC device with verticalinterfaces (adjacent to a crackstop on the perimeter of a chip) whichcontrols cracks generated during steps such as side processing of thedevice, e.g. dicing, and controls cracks when the chips are in serviceby preventing a crack from penetrating the crackstop. The verticalinterface is comprised of a material that prevents cracks from damagingthe crackstop by deflecting cracks away from penetration of thecrackstop, or by absorbing the generated crack energies. The verticalinterface may be a material that allows advancing cracks to lose enoughenergy so they cannot penetrate the crackstop. The vertical interfacescan be implemented in a number of ways such as, vertical spacers ofrelease material, vertical trenches of release material or verticalchannels of the release material. There can be voids in the materialsuch as an ultra low-k dielectric layer formed in a vertical trenchjuxtaposed with the crackstop.

The Abstract of Japanese Patent Publication 2004-111946 of Kubo et alentitled “Laser Dicing Equipment and Dicing Method” describes use oflaser heads to perform dicing. For example, the laser heads are indexedfrom both ends to the center of a wafer, or from the center of the waferto both ends. Alternatively, the laser heads are arranged separated fromeach other by a prescribed number of lines and indexed in the samedirection, and two lines are carved into the wafer throughout itssurface.

US2006/0057822A1 (commonly assigned) of Daubenspeck et al. entitled“Chip Dicing” describes a semiconductor structure and method for chipdicing, wherein first and second device regions of first and secondchips are formed in and at the top of the semiconductor substrate. Thechips are separated by a semiconductor border region of thesemiconductor substrate. N interconnect layers are formed directly overthe semiconductor border region and first and second device regions,where N is a positive integer, with each of N interconnect layerscomprising an etchable portion directly above the border region.Etchable portions of the N interconnect layers form a continuousetchable block removed by etching. Then a laser cuts through thesemiconductor border region forming an empty space by removal of thecontinuous etchable block to separate the first chip from the secondchip.

The Abstract of Japanese Patent Publication 2005-109322 of Yakasuki etal describes a “Laser Beam Dicing Device” with the laser head of a laserbeam dicing device that includes a plurality of laser oscillators andlight-condensing means which condense oscillated laser light beamsindividually and an optical path collecting means which collects thelaser light beams onto one optical axis. The laser beam dicing device isuseful with various processes, e.g. formation of a multilayered reformedarea in a wafer, a composite process by which the formation of thereformed area in the wafer and the cutting of the die attaching tape areperformed simultaneously, or the like, with the laser light beamsconverging at different positions.

In Guthrie, an air gap is described formed in a structure that extendsto the active device region to the edge of a gate electrode and over theedge thereabove but not reaching down to the surface of the substratetherebelow. We have discovered that there is a problem that such astructure cannot prevent delaminations.

Fitzsimmons et al provides a void down to a cap layer with no indicationof what is formed below the cap layer. The application initiallymentions substrates but fails to show a substrate or indicate what isbelow the cap layer.

As stated above, a key requirement for preventing these new failuremechanisms described above is to limit the propagation distance that aflaw (generated during the dicing process) can propagate before itencounters the barrier (crackstop/MOB) structure. While there are anumber of potential solutions to this problem, heretofore all solutionsknown require either a loss in productivity (reduction in number ofchips per wafer) or a loss in I/O density (due to a redesign of aControlled Collapse Chip Connection (C4) layout).

SUMMARY OF THE INVENTION

An object of this invention is to provide a structure that inhibitscracks from reaching the active chip BEOL structures.

Another object of this invention is to form a crack resistant chip edgein an IC device which provides robustness to defects generated duringdicing from a wafer to form chips therefrom and subsequent packaging andthermal stress.

Similarly it is an object of this invention to provide a method formanufacturing a crack resistant chip edge in an IC device.

In accordance with the present invention, a hollow chip edge trench isjuxtaposed with the crackstop MOB structure. The trench is formed in theBEOL structure and must extend into the FEOL regions in the siliconsubstrate where it will be filled with an underfill material and providea mechanical interlock. Were Guthrie's process taken with low-k (LK) andultra low-k (ULK) devices, the BEOL structure would be ripped off by themismatch in CTE which is what our present invention prevents. Thus wehave discovered that it is the depth of penetration into the siliconsubstrate and the interlocking of the underfill with the siliconsubstrate that is a key difference when the present invention iscompared with the structure and method of Guthrie. Accordingly, we havediscovered that the underfill material must be anchored into the siliconto provide any benefit.

The present invention provides a structure and a method whereby dicingdamage is prevented from reaching the crackstop region in aninterconnect, by creation of a protective firewall. This firewall may becreated using different methods. One particularly useful method is touse laser etching to create a laser channel. Preferably, the laserchannel is created with the closest possible proximity to the crackstop,which in turn reduces the energy available for any potential crack topropagate (in this instance the crack would be one that is created as aresult of the laser channel, but this in itself is an unlikely event).Such a laser channel is referred to hereinafter as an Ultra DeepIsolation Trench (UDIT.)

Fundamentally, according to the method of this invention and structureproduced thereby, dicing may be performed by conventional means (e.g.saw dicing) in the appropriate zone for chip dicing. Dicing can also beperformed by a combination of methods (laser dicing and saw dicing) inthe appropriate zone for chip dicing. Laser channel creation close tothe crackstop, creates a barrier for preventing any cracks initiated bythe dicing above from penetration thereof and reaching the crackstop.Any micro-cracks created by laser channeling action (unlikely in thefirst place), will have a very short distance to travel before reachingthe crackstop, thus preventing a high potential energy crackingsituation from developing.

The edge structure of this invention can be applied to any semiconductorchip or semiconductor device that is removed from a larger plurality ofdevices such as a silicon semiconductor wafer as is commonly done inmanufacturing FET devices. This invention is also directed to a processfor making a chip edge structure.

In accordance with this invention a chip edge consists of an isolationtrench or isolation trenches that penetrate into the semiconductor (Si)substrate adjacent to the crackstop and moisture/oxidation barrieractive area (AA) of the device. The area outside the isolation trench ortrenches may have the same levels as present in the active device levelor they may be removed.

This invention provides an IC structure in chip form with a chip edge inaccordance with this invention located outside the chip Active Area (AA)where the definition of is the area AA comprises the area inside thecrackstop/moisture-oxidation barrier which typically spans all levels ofa solid metal BEOL structure or a plurality of solid metal structures.The edge structure of this invention can be applied to any chip ordevice which is removed from a larger plurality of devices such as a Siwafer as is common in CMOS devices.

A key requirement for stopping these new failure mechanisms describedabove is to limit the propagation distance which a flaw generated duringdicing process can propagate before it encounters the crackstop/MOBstructure. While there are a number of potential solutions to thisproblem, all known solutions other than the chip edge of the presentinvention require either a loss in productivity (reduction in number ofchips per wafer) or a loss in I/O density (due to a redesign of aControlled Collapse Chip Connection (C4) layouts).

Glossary

BLoK: a Si—C—H compound serving as a hard mask capping layer genericallyreferred to as silicon carbide;

N-BLoK: mostly Si—C—H—N; serving as a hard mask capping layer,generically referred to as silicon carbonitride or nitrogen dopedsilicon carbide;

SiCOH: hydrogenated silicon oxycarbide, which is a low-k, dielectricfilm -comprising at least atoms of silicon (Si), carbon (C), oxygen (O,)and hydrogen (H);

pSiCOH: porous hydrogenated silicon oxycarbide which is a low-k,dielectric film comprising porous SiCOH which contains molecular scalevoids (i.e., nanometer-sized pores), which reduce the dielectricconstant of the SiCOH dielectric material.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be better understood by reference to the detaileddescription of the invention when taken together with the attacheddrawings, many of which represent the edge of a chip in cross-sectionand are not meant to represent the entire chip but only a portion of thechip, wherein:

FIG. 1A a schematic, sectional, fragmentary view of a prior art CMOS FETsemiconductor device, in an advanced stage of manufacture, shown formedin and upon the surface of a semiconductor substrate prior to the stepof dicing.

FIG. 1B depicts the prior art device of FIG. 1A after the dicing stepwhich splits the device first and second chips by forming a dicingchannel therein.

FIG. 2A is a chart which shows the decreasing of the cohesive strengthof the ILD of a semiconductor chip as the dielectric constant decreases.

FIG. 2B is a chart which shows the energy imparted to dielectric layersdue to the packaging material as a function of the defect size, i.e.length, of a flaw which is created during dicing and which propagatesduring reliability stressing.

FIG. 3A shows an elevational sectional view taken along line 3A-3A′ inFIG. 4 of an embodiment of this invention comprising a modification ofthe device of FIG. 1A in Ultra Deep Isolation Trenches (UDITs) have beenadded.

FIG. 3B shows the device of FIG. 3A after dicing through the channel toseparate the first chip from the second chip and the remainder of thechips not shown in FIG. 3A.

FIG. 3C shows the diced chips of FIG. 3B after depositing a blanketunderfill layer thereover to protect the diced chips.

The combination of FIGS. 3A, 3B′, and 3C′ illustrate an alternative tothe process of FIGS. 3B and 3C with reference to FIG. 10B which is aflow chart for an alternative process to that of FIG. 10A.

FIG. 4 is a plan view of a device in accordance with this invention witha first chip juxtaposed with a second chip with barrier rings aroundactive areas of each of the chips, and UDITs which surround the barrierrings, separating the barrier rings from a chip-to-chip dicing channellocated between the first and second chips.

FIG. 5A is a sectional elevation taken along line 5A-5A′ in FIG. 4,which shows the second chip after dicing and prior to formation of anunderfill layer thereover.

FIG. 5B shows the second chip of FIG. 5A after both forming of anunderfill layer over the top surface of the chip and joining the chip toa package.

FIG. 6A shows the device of FIG. 5A with the outside area between theUDIT trench and the diced edge which has been recessed to remove theinterconnect layer outboard from the UDIT trench.

FIG. 6B shows the device of FIG. 6A after forming of an underfill layerover the top surface of the chip and joining the chip to a package.

FIG. 7A shows a modification of the device of FIG. 5A in which severalUDIT trenches have been formed, between the barrier structure and thechip edge.

FIG. 7B shows the device of FIG. 7A after both forming of an underfilllayer over the top surface of the chip and joining the chip to apackage.

FIG. 7C is a plan view of the second chip of FIG. 7B with a barrier ringsurrounding the active areas of the second chip, and with three UDITsformed with one inside the other around the barrier ring aside from achip-to-chip dicing channel.

FIGS. 8A and 8B show a further modification of the embodiment of theinvention shown in FIGS. 5A and 5B.

FIGS. 9A and 9B show an embodiment of the invention with a trench cut atan obtuse angle in the top surface of the substrate, providing a benefitsimilar that obtained with the embodiment of the invention shown inFIGS. 8A and 8B.

FIG. 10A is a process flow chart for the process of FIGS. 3A, 3B and-3C.

FIG. 10B is a process flow chart for the process of FIGS. 3A, 3B′-3C′.

FIG. 11 is a chart of the Energy Release Rate vs. Delamination Lengthshowing that while a second underfill UF2 has a lower energy releaserate than a first underfill UF1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3A is an elevational sectional view taken along line 3A-3A′ in FIG.4 which shows a semiconductor device 10 comprising an embodiment of thisinvention which is a modification of the device 10 of FIG. 1A. For themost part, the semiconductor device 10 of FIG. 3A is identical to thedevice 10 of FIG. 1A with similar features being identified similarly bythe same reference indicia with the same meanings. The device 10includes the silicon semiconductor substrate 12, an active device FEOLregion 14 containing structures, e.g. CMOS FET devices, portion of whichare formed in the silicon semiconductor substrate 12 and portions ofwhich are formed upon the top surface 16 thereof. The BEOL(interconnect) layer 15 is formed over the top surface 17 of the activedevice layer 14. The BEOL structure 15 comprises an interconnectstructure comprising an Inter Level Dielectric (ILD) material and copperconductors embedded in the ILD material.

However, in FIG. 3A the semiconductor device 10 is significantlydifferent from the semiconductor device 10 of FIG. 1A because of theaddition of the two Ultra Deep Isolation Trenches (UDITs) 60A/60Bthereto in accordance with this invention, which extend down from thetop surface of the semiconductor substrate 12 of the semiconductordevice 10 and only partially through the semiconductor substrate 12. TheUDIT 60A forms a frame which surrounds the crackstop barrier structure50A as well as the active areas AA of the chip 10A. Similarly, the UDIT60B forms a frame which surrounds the crackstop barrier structure 50B aswell as the active areas AA of the chip 10B. The crackstop barrierstructured 50A and 50B are located between the dicing channel 130 andthe active area (AA) of each of the chips 12A/12B, respectively. As inFIGS. 1A and 1B, each of the crackstops 50A/50B extends entirely throughthe BEOL interconnect layer 15 to the top surface 17 of the activedevice FEOL region 14.

Referring again to FIG. 3A, it can be seen that the UDIT trenches60A/60B extend down from the top surface 18 through the BEOLinterconnect layer 15 and active device FEOL region 14 therebelow, downto a depth 70 below the top surface 16 of the silicon semiconductorsubstrate 12. Thus the UDIT trenches reach only partially down into thesilicon semiconductor substrate 12, but to a significant depth thereinbelow the top surface of the silicon semiconductor substrate 12. TheUDIT trenches 60A/60B are deep and open to receive an underfill materialtherein to protect the first and second chips 10A/10B from subsequentdamage.

The UDIT trenches 60A/60B can be formed by a subtractive process, e.g.saw cutting to form Saw Cut UDITs (SCUDITs), or laser scribing to formLaser Scribed UDITs (LSUDITs). Referring to FIG. 10A, the process offorming device 10 of FIG. 3A starts with step AA which leads to step AB.In step AB the active device FEOL region 14 is formed on the top surface16 of the semiconductor substrate 12 of the semiconductor device 10.Step AC involves forming an interconnect structure 15 over the topsurface 17 of the active device FEOL region 14 as is well understood bythose skilled in the art. Both FIGS. 3A and 4 show a space 132 betweenthe two crackstop barrier structures 50A/50B which frame the first andsecond chips 10A/10B.

In step AD in FIG. 10A, the UDITs 60A/60B are formed in semiconductordevice 10 by saw cutting from the top surface 18 down through theinterconnect structure 15 and the active device FEOL region 14 into thesubstrate 12 by one of several techniques. With saw cutting Saw CutUDITs (SCUDITs) are formed. By employing laser scribing, Laser ScribedUDITs (LSUDITs) are created. Alternatively, any other subtractiveprocess can be employed to form the UDIT trenches 60A/60B framing thecrackstop barrier structures 50A/50B. The UDIT trenches 60A/60B arelocated between the dicing channel 130 and the frames provided by thecrackstop barrier structures 50A/50B which also surround the activeareas AA.

In other words, the crackstop barrier structures 50A/50B which frame andsurround both of the active areas AA are framed and surrounded in turnby the UDIT trenches 60A/60B which in FIG. 3A are analogous to emptymoats. The UDIT trenches 60A/60B are separated from the dicing channel130 by the margin TD, i.e. the trenches 60A/60B are separated from wherethe diced edge of the chip may be by the margin TD. In the otherdirection towards the active areas AA, the UDIT trenches 60A/60B areseparated from the crackstop barrier structures 50A/50B by therelatively narrow Delamination Length DL.

In FIGS. 3A/3B-9A/9B, the delamination length DL is the distance betweenthe UDIT 60A/60B and the adjacent crackstop barrier structures 50A/50B.The greater the length DL, the greater is the amount of the energyreleased in the interconnect layer 15A/15B which tends to increase theprobability of failures.

FIG. 3B shows the semiconductor device 10 of FIG. 3A after the step ofdicing through the channel 130 in FIGS. 3A and 4 in accordance with stepAE in FIG. 10A to separate the first chip 10A from the second chip 10B,prior to forming an underfill layer 140 shown in FIG. 3C. The dicingprocess also separates the remainder of the chips not shown in FIG. 3Afrom each other. As in FIG. 1B, chip edge surfaces 110 are formedapproximately along the vertical edges of the chip-to-chip dicingchannel 130 where material has been removed. The first chip 10A includesthe interconnect layer 15A, the active device layer 14A and thesemiconductor substrate 12A including the active devices of the firstchip 10A therein. The second chip 10B includes the interconnect layer15B, the active device layer 14B and the semiconductor substrate 12Bincluding the active devices of the second chip 10B therein.

In FIG. 3C the diced chips 10A/10B of FIG. 3B are shown after depositionthereover of a blanket underfill layer 140, in accordance with step AFin FIG. 10. The blanket underfill layer 140, which is formed to protectthe diced chips 10A/10BA, covers the top surfaces 18 of both of thechips 10A/10B and is shown filling the UDITs 60A/60B completely. Asshown in FIG. 3C, the blanket underfill layer 140 covers the chips10A/10B completely thereby providing a protective coating covering thepreviously exposed top surfaces 18 and the chip edge surfaces 110 ofchips 10A/10B on the sidewalls thereof. In other words, the blanketunderfill layer 140 reaches down to fill the UDIT trenches 60A/60B andcovers the diced chip edge surfaces 110 on the sidewalls of the dicedchips 10A/10B.

Alternative Process

An alternative to the process of FIGS. 3B and 3C is illustrated by bothFIG. 3B′ and FIG. 3C′ with reference to the flow chart in FIG. 10Bwherein steps AA-AD are identical to those of FIG. 10A.

In FIG. 3B′, in accordance with step AE′ in FIG. 10B the semiconductordevice 10 of FIG. 3A of step AD has been coated with a blanket underfilllayer 140 prior to the step of dicing step. In this case the device 10is completely covered with a blanket underfill layer 140 prior to thedicing step. Note that as with FIG. 3C, the underfill layer 140 coversthe top surface 18 of the BEOL structure 15 of semiconductor device 10and completely fills the UDIT trenches 60A/60B, but of course it doesnot cover the sidewalls 110 (i.e. soon to be formed sidewalls of thediced chips 10A/10B, which have not reset been formed at this stage ofthe process of FIG. 10B). Nevertheless, at the end of step AE′, theblanket underfill layer 140 covers the top surfaces 18 of the BEOLstructure 15 and completely fills the UDIT trenches 60A/60B.

Then referring to FIG. 3C′, the device of 3B′ is shown (as with FIG. 3B)with the chips 10A/10B separated by dicing with the diced chip edges110, i.e. sidewalls, formed along the dicing channel 130 where materialwas removed in accordance with step AF′ in FIG. 10B. The first chip 10Aincludes the interconnect layer 15A, the active device layer 14A and thesemiconductor substrate 12A including active devices therein. The secondchip 10B includes the BEOL structure 15B, the active device layer 14Band the semiconductor substrate 12B including active devices therein. Aswith FIG. 3C, the underfill layer 140, which covers the top surface ofthe semiconductor device 10 and fills all of the UDIT trenches remainsin place including completely covering the top surfaces 18 of the BEOLstructures 15A/15B of the chips 10A/10B and completely filling the UDITs60A/60B, but leaving the diced chip edges 110 (sidewalls) of the dicedchips 10A/10B uncovered.

FIG. 4 shows a plan view of a semiconductor device 10 of FIG. 3A priorto dicing and formation of the underfill layer 140 including the firstchip 10A and the second chip 10B. A preferred embodiment of the chipedge in accordance with this invention is shown in FIG. 4.

First Preferred Embodiment

FIG. 5A is a sectional elevation, taken along line 5A-5A′ in FIG. 4,which shows an enlarged view of the second chip 10B after forming theUDIT 60B located between the edges 110 and the crackstops 50B; and afterperforming the dicing step in accordance with the process steps of FIG.10A; but prior to forming an underfill layer 140. As is conventional,the silicon substrate 12B of the second chip 10B is lightly doped. Afirst FET 22B and a second FET 24B are shown schematically formed in thetop surface of the active device layer 14B of the second chip 10B. Thereare metal interconnects (preferably copper conductors) in the form ofhorizontally extending metal lines 44 within several stacked dielectriclayers 30 in the BEOL structure 15B. As will be well understood by thoseskilled in the art, the metal interconnects are connected together bythe vertically extending metal vias 45. External connections areprovided to the FET 22B by the combination of the metal interconnects42A-42D and the intermediate metal vias 45 which provide connectionsbetween the metal interconnect lines. Similarly, external connectionsare provided to the FET 24B by the metal interconnect lines 44A-44D andthe associated intermediate metal vias 45, as will be well understood bythose skilled in the art.

The capping layers 30 are formed of a hard mask material such as N-BLoK.The low-k dielectric layer 31 comprises pSiCOH (porous SiCOH.) AnNBloK/pSiCOH interface 30/31 is created when a hard mask layer 30 isdeposited onto a previously deposited dielectric layer 31 containinglower level metal lines 42/44 and the vias 45. An N-BLoK capping layer30 is formed on the top surface of the FEOL region 14B and on top ofeach dielectric layer 31. Dielectric layer 31 contains metal lines 42/44and so an N-BloK/pSiCOH interface 30/31 is formed when each cappinglayer 30 is deposited on an underlying dielectric layer 31. ThepSiCOH/N-BloK 31/30 interface is created when pSiCOH is deposited on topof N-BloK. The interface has lower toughness than N-BloK/pSiCOH 30/31interface, and the adhesion is shown in FIG. 11 as line 143.

Referring again to FIG. 5A, as indicated above, the BEOL structure 15Bof the second chip 10B consists of a stack of a plurality of ILDdielectric layers 31 composed of a low-k dielectric material such aspSICOH separated by cap layers 30 composed of a material such as NBLoK.On the left, a crackstop/MOB 50B is shown between the first FET 22B onthe right and the UDIT trench 60B on the left. The plurality ofdifferent ILD layers 30 in the BEOL structure 15B may have a pluralityof different dielectric constants but should consist of at least onedielectric layer with a bulk dielectric constant (k) less thanapproximately 3.3.

In summary, the embodiment of FIG. 5A consists of the substrate 12B, theFEOL region 14B and the BEOL structure 15B, the crackstop/MOB 50B, andthe UDIT trench 60B surrounding and proximate to the crackstop/MOB 50B.The FEOL region includes portions of the active FET devices 22B/24B. TheBEOL structure includes the multilayer ILD stack 15B, the metal vias 45and the metal interconnects 42A-42D, 44A-44D. In FIG. 5A, on the left ofthe semiconductor device 10B, there is an outer margin 62 with the widthTD outside of the trench 60B on the right and the diced chip edge 110 onthe left.

Important parameters relative to prevention of damage due to cracks inthe semiconductor device 10B are the delamination length DL comprisingthe inner margin 64 between the crackstop/MOB 50B and the UDIT trench60B and the distance TD (which spans the outer margin 62) from the UDITtrench 60B to the diced chip edge 110. The outer margin 62 extends fromthe outside of the UDIT trench 60B and the proximate chip edge 110. Thetrench of the UDIT trench 60B reaches down through the ILD layers30A-30D to a depth 70 below the top surface of the FEOL region 14B ofthe substrate 12B to provide enhanced protection of the chip 10B fromdamage caused by cracking.

The trench region 60B, which is next to the crackstop/MOB 50B, has awidth of between about 1 μm to about 80 μm, which may be created by alaser scribe, a mechanical saw, or any such other suitable cuttingmethods so as to give the structure shown in FIG. 4. The depth 70 of theUDIT trench below the top surface of the BEOL region 14B of thesubstrate is preferably from about 1 μm to about 200 μm and may beoptimized for reliability. The distance comprising the DelaminationLength DL between the crackstop/MOB 50B and the UDIT trench 60B ispreferably within the range from about 0 μm to about 40 μm. The distanceTD from the outer edge of UDIT trench 60B to the diced edge 110 iswithin the range between about 0 μm and about 200 μm.

FIG. 5B shows the second chip 10B (FIG. 5A) after performing processsteps in accordance with FIG. 10A; with the dicing step followed bydepositing the underfill layer 140 completely covering the semiconductordevice 10B and joining the device to a package 80. The underfill layer140 completely covers the top surface of the ILD stack 30 of theinterconnect 15B and completely fills the UDIT trench 60B as well ascovering the chip edge 110, reaching around the outer margin 62 toprotect the chip 10B by inhibiting damage from dicing and chip packaginginteraction failures in the interconnect structure 15B among otherportions of the chip 10B. After formation of the underfill layer 140,the package 80 is bonded to the chip 10 in a conventional manner by C4bonds or the like obscured by the underfill 140.

The underfill layer 140 may be composed of a material such as either UF1or UF2. Both UF1 and UF2 materials are underfill compounds with eachhaving a different modulus and a different CTE value; but UF1 is thepreferred underfill material. Referring to FIG. 11, while UF2 has alower energy release rate (curve 142) than UF1 (curve 141), UF2 isunsatisfactory because it is prone to cause delamination due to C4fatigue in interconnect structures. The UF materials are organicpolymers filled with silica beads and both UF1 and UF2 haveapproximately the same percentage of silica filler. Line 143 representsthe adhesion at the interface between the low-k dielectric layer 31 andcap layer 30, where the low-k dielectric is pSiCOH in FIGS. 5A/5B andFIG. 11.

TABLE I Material Properties of Underfill Materials UF1 and UF2 GlassTransition CTE Below Tg Modulus Below Tg Material Temperature (Tg)(ppm/C.) (GPa) UF1 94° C. 28 10 UF2 60° C. 35 8

Second Preferred Embodiment

FIG. 6A shows the device of FIG. 5A with the outer margin 62 indented.i.e. recessed outboard from the UDIT trench between the UDIT trench 60Band the diced edge cut back, thereby forming a recessed region 62A ofthe BEOL structure 15B in the outer margin 62 thereof. In that portionof the outer margin 62 the interconnect layer 15B has been removed bymeans such as laser scribe, mechanical saw dicing or other such suitablemethods so as to give the structure in FIG. 4 and the chip edge 110.Preferably the recessed region 62A which is located aside from the UDITtrench 60B′ and ILD region 30 has been formed by removing that portionof the BEOL structure 15B down to the top surface of the siliconsubstrate 12B by a laser ablation process.

FIG. 6B shows the semiconductor device 10B of FIG. 6A after depositionof the underfill layer 140 and after joining the device to a package 80.The underlayer 140 completely covers the top surface of the BEOLstructure 15B and completely fills the UDIT trench 60B′, covering theexposed surface of the semiconductor substrate 12B in the outer margin62, as well as covering the chip edge 110, reaching around the outermargin 62 to protect the chip 10B by inhibiting damage from dicing andchip packaging interaction failures in the interconnect structure 15Bamong other portions of the chip 10B. After formation of the underfilllayer 140, the package 80 is bonded to the chip 10 in a conventionalmanner by C4 bonds or the like obscured by the underfill 140.

Third Preferred Embodiment

FIGS. 7A, 7B and 7C show sectional views of a modification of thesemiconductor device 10B of FIG. 5A in which a plurality of parallelUDIT trenches 60B, 61B and 62B have been formed, between the barrierstructure 50B and the chip edge 110. FIG. 7B shows the semiconductordevice 10B of FIG. 7A after deposition of the underfill layer 140,completely covering the top surface of the BEOL 15B filling the parallelUDIT trenches 60B, 61B and 62B and after joining the device to a package80. In the plan view of FIG. 7C, the narrow UDIT trenches 60B, 61B and62B (which are of equal depth) surrounding the barrier structure 50B andthe inner UDIT trenches have successively larger dimensions of lengthand width as shown in the plan view of FIG. 7C with widths as describedabove and where the area outside each trench may be intact or removed bypreviously described processes. An additional benefit of the chip edgein accordance with this invention may be realized once the chip ispackaged which typically entails covering the chip with a moldingcompound (for a wirebond type application) or an underfill (for a C4type application). In the embodiment of FIGS. 7A-7C, the moldingcompound or the underfill layer 140 fills the trenches 60B, 61B, and62B, as shown in FIG. 7B. The molding compound or underfill layer 140provides a mechanical interlock between the chip 10B and the package andreduces the effective stress on the dielectric materials. Afterformation of the underfill layer 140, the package 80 is bonded to thechip 10 in a conventional manner by C4 bonds or the like obscured by theunderfill 140.

Fourth Preferred Embodiment

FIGS. 8A and 8B show a further modification of the embodiment of theinvention shown in FIGS. 5A and 5B. This embodiment is particularlyapplicable to dicing procedures that are performed by a laser. Onepotential application that would lead to the structure in FIGS. 8A and8B is to create a trench through either saw or laser dicing and thenmake a second pass along the trench 60D with a laser. In FIGS. 8A and8B, the second pass through the trench with the laser is identified bythe additional feature where the trench 60D is expanded, i.e. flaredout, to form a trough 120 at the bottom of the trench 60D wider than thewidth of the portion of the trench 60D thereabove. FIG. 8B shows thesemiconductor device 10B of FIG. 8A after deposition of the underfilllayer 140 completely covering the top surface of the BEOL 15B fillingthe parallel UDIT trench 60D as well as its trough 120 and after joiningthe device to a package 80. There is a rounded cross section at thebottom of the trench 60D which is also filled with underfill or moldingcompound during packaging as shown in FIG. 8B. After formation of theunderfill layer 140, the package 80 is bonded to the chip 10 in aconventional manner by C4 bonds or the like obscured by the underfill140.

Fifth Preferred Embodiment

FIGS. 9A and 9B show an embodiment of the invention providing a benefitsimilar that obtained with the embodiment of the invention shown inFIGS. 8A and 8B. FIG. 9B shows the semiconductor device 10B of FIG. 9Aafter deposition of the underfill layer 140 completely covering the topsurface of the BEOL 15B filling its angled UDIT trench 60E and afterjoining the device to a package 80. In FIGS. 9A and 9B UDIT trench 60Eis cut slanted at an obtuse angle with respect to the top surface of thesemiconductor substrate 12B and undercutting substrate 12B, either bytilting the cutting device (laser or saw blade not shown) or thesemiconductor substrate 12B or both.

The foregoing description discloses only exemplary embodiments of theinvention. Modifications of the above disclosed apparatus and methodswhich fall within the scope of the invention will be readily apparent tothose of ordinary skill in the art. While this invention has beendescribed in terms of the above specific exemplary embodiment(s), thoseskilled in the art will recognize that the invention can be practicedwith modifications within the spirit and scope of the appended claims,i.e. changes can be made in form and detail, without departing from thespirit and scope of the invention. Accordingly, while the presentinvention has been disclosed in connection with exemplary embodimentsthereof, it should be understood that changes can be made to provideother embodiments which may fall within the spirit and scope of theinvention and all such changes come within the purview of the presentinvention and the invention encompasses the subject matter defined bythe following claims.

1. A method of forming a semiconductor product comprising asemiconductor substrate having a top surface and a bottom surfaceincluding a semiconductor chip with said semiconductor substrate havinga top surface and a perimeter; an active device (FEOL) layer on said topsurface, a BEOL layer on top of said FEOL layer, and a barrier formed insaid chip within said perimeter; comprising the step of cutting a trenchextending down through said top surface of said semiconductor product,but extending only partially down into said substrate between saidbarrier and the outermost of said perimeter, prior to performing thefollowing steps: forming a blanket underfill layer over said productcompletely covering said semiconductor product and completely fillingsaid trench, and dicing said semiconductor product into chips.
 2. Amethod of forming a semiconductor product comprising a semiconductorsubstrate having a top surface and a bottom surface including asemiconductor chip with said semiconductor substrate having a topsurface and a perimeter; and a crack stop barrier formed in said chipwithin said perimeter, and with an active device layer and aninterconnection structure above said substrate; comprising the step ofcutting a trench extending down through said top surface of saidsemiconductor product, but extending only partially down into saidactive device layer or said substrate between said crack stop barrierand the outermost of said perimeter, prior to performing the followingsteps: forming a blanket underfill layer over said product completelycovering said interconnection structure and completely filling saidtrench, and dicing said semiconductor product into chips.
 3. The methodof claim 2 including: spacing said trench laterally with respect to saidtop surface of said substrate from said barrier, and spacing said trenchfrom said diced edge of said chip.
 4. The method of claim 3 wherein saidunderfill layer comprises an organic polymer filled with silica beads.5. The method of claim 2 wherein a plurality of trenches are formednested one inside another in a sequence of trenches of increasinglateral dimensions are formed cut into said top surface of saidsemiconductor chip surrounding said barrier, between said perimeter andsaid barrier.
 6. The method of claim 5 wherein said underfill layercomprises an organic polymer filled with silica beads.
 7. The method ofclaim 2 wherein said trench is slanted at an angle with respect to saidtop surface.
 8. The method of claim 7 wherein said underfill layercomprises an organic polymer filled with silica beads.
 9. The method ofclaim 2 wherein said step of forming said trench and said step offorming said underfill layer are performed prior to said step of dicingsaid semiconductor product into chips.
 10. The method of claim 9 whereinsaid underfill layer comprises an organic polymer filled with silicabeads.
 11. The semiconductor product of claim 2 comprising: forming asemiconductor device in said semiconductor product; and forming aninterconnection structure above said active device layer containingdielectric layers, interconnect lines and vias.
 12. The method of claim11 wherein said underfill layer comprises an organic polymer filled withsilica beads.
 13. The method of claim 11 including forming said barrierextending through said interconnection layer into contact with saidsemiconductor substrate.
 14. The method of claim 13 wherein saidunderfill layer comprises an organic polymer filled with silica beads.15. The method of claim 11 wherein said interconnection structureincludes a low-k dielectric material.
 16. The method of claim 15 whereinsaid low-k dielectric material comprises porous hydrogenated siliconoxycarbide (pSiCOH).
 17. The method of claim 16 wherein said underfilllayer comprises an organic polymer filled with silica beads.
 18. Themethod of claim 15 wherein said underfill layer comprises an organicpolymer filled with silica beads.
 19. The method of claim 11 whereinsaid interconnection structure is recessed down to said substrateoutboard from said trench.
 20. The method of claim 19 wherein saidtrench has a bottom which is flared outwardly forming a trough widerthan said trench at the bottom of said trench and wider than the widthof said trench thereabove.
 21. The method of claim 20 wherein saidunderfill layer comprises an organic polymer filled with silica beads.22. The method of claim 19 wherein said underfill layer comprises anorganic polymer filled with silica beads.